JPS63121758A - Method for measuring zero phase current by using electro-optic effect element - Google Patents

Abstract

PURPOSE:To surely insulate electro-optical effect elements against ground potential and to make measurement by disposing search coils to the respective side faces of a three-phase aerial distribution line, impressing an induced voltage to the electro-optic effect elements of an optical voltage sensor and making electrical conversion through an optical fiber. CONSTITUTION:The search coils 1, 2, 3 are disposed in proximity to conductors R, S, T of the three-phase aerial distribution line. The voltage sensor 5 is assembled in a housing 4 consisting of an insulator and the housing 4 is supported by a support 29 which is supported by a pole 22. The sensor 5 is constituted by linearly disposing 3 pieces of the electro-optic effect elements 7 and a quarter wavelength plate 8 between a polarizer 6 and an analyzer 9. Light is applied by the optical fiber 10 to the polarizer 6 and the fiber 11 for photodetection is disposed on the exit side of the analyzer 9. The other ends of the fibers 10, 11 are connected to a signal processor 12. The processor 12 is disposed on the ground or in the position near the ground. The measurement is thus made by surely insulating the sensor against the ground potential.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a zero-sequence current measuring method using an electro-optic effect element.

[Prior art and problems] A current transformer for detecting zero-sequence current is a current transformer that connects three phase conductors R, S, and T all at once and connects them through the conductor through-hole of a through-type current transformer 20, as shown in Fig. 3. It is a type that passes through.

Since such a feedthrough current transformer 20 is at ground potential, when it is directly applied to an insulated wire forming a three-phase overhead distribution line, the insulated wire is brought into direct contact with the ground potential. However, overhead insulated wires are not designed to be insulated so that they may come into direct contact with the ground, and there is a problem in that they cannot be directly applied to overhead insulated wires of E, EKV or higher.

In order to detect the zero-sequence current by attaching a zero-sequence current transformer to an overhead insulated wire, a configuration as shown in FIG. 4 is adopted.

As shown in the figure, reference numeral 21 indicates an overhead insulated electric wire 22 for power distribution, an electric pole, and 23 an insulator.The overhead insulated electric wire 21 is held on both sides of the electric pole 22 by insulators 23. The underground cable cables 24 are connected and passed through the through holes of the through-type current transformers 20 attached to the utility poles 22 in three groups.

However, such a configuration requires a considerable amount of space because it uses an underground cable cable 24 and the current transformer 20 is installed at a location away from the overhead insulated wire 21.
There is a problem that it spoils the aesthetic appearance.

[Objective and Structure of the Invention] As described above, the present invention solves the problems that occur when a three-phase distribution line using overhead insulated wires is passed through a feedthrough current transformer all at once, and if the above-mentioned improvement measures are taken, the installation can be easily achieved. This was done with the aim of further improving the space-consuming, high-cost, and unsightly appearance of the three-phase overhead insulated wires that form the three-phase overhead distribution line. The current of each insulated wire is converted into a voltage signal by placing a A voltage signal from the search coil is applied to the electro-optic effect element, the light projected from the polarizer is passed through the three electro-optic effect elements and the quarter-wave plate, and is received via the analyzer. This is a zero-sequence current measurement method characterized by electrical conversion via an optical fiber.

The present invention will be explained below with reference to embodiments shown in the drawings.

In Fig. 1, 1.2.3 is a search coil, and the conductors R,
Place it close to S and T. Reference numeral 5 denotes a voltage sensor, which is assembled in a casing 4 made of an insulator.

The voltage sensor 5 includes three electro-optic effect elements (Pockels effect elements) 7. A quarter wavelength plate 8, a polarizer 6 and an analyzer 9
The polarizer 6 is arranged linearly between the polarizer 6 and the optical fiber! 0 provides light, and a row of optical fibers for receiving light is arranged on the output side of the analyzer 9.

be done. The signal processor 12 includes a light emitting diode that provides light to the optical fiber 10, and a photodiode that receives light from the analyzer 9 and converts it into an electrical quantity, and connects the optical fiber 10 to the ground. The signal processor 12 is arranged at or near the ground so that the length of II is long, and the electrically converted measurement output is extracted from this.

[During normal operation, the characteristics of the search coil 1.2.3 and each electro-optical element 7 are aligned in advance, and when the distribution line is in balanced operation, three-phase currents of equal magnitude flow, and the search coil 1.2.3 has the same characteristics. If the current is adjusted so that voltages of equal magnitude are generated, the voltages of each of the three phases are shifted by 120a, so that the current passes through the polarizer 6 and passes through each electro-optic effect element 3 in this state. The projected light is substantially polarized by the polarizer without being deflected at all by the electric field caused by the balanced currents, which have the same magnitude and whose phases differ by 120 degrees, which are applied to each electro-optic effect element 3. It reaches the 1/4 wavelength plate, is circularly polarized, passes through the analyzer, and is modulated [at the time of an accident] On the other hand, when each phase current is different, the voltage applied to each electro-optic effect element 3 is different. The projected light polarized by the polarizer is polarized in an unbalanced manner in each electro-optic effect element, reaches the 174-wave plate, and the light that is circularly polarized and exits the analyzer is larger than that due to the previous balanced current. Alternatively, the zero-sequence current can be detected by a photodiode.

FIG. 2 shows the installation of equipment for carrying out the invention.

For example, for a three-phase distribution line consisting of three overhead insulated wires supported by an insulator 26 on a utility pole 22 and a arm 25, the arm 25
3 search coils 1.2.3 made of an insulator.
A rod-shaped support body 27 holding a .
It is connected to each electro-optic effect element (Fig. 1) housed in the. The housing 4 is supported by a support 29 supported by a utility pole 22, for example, and an optical fiber cable 30 is pulled out from the housing 4, and is connected to a signal converter installed on or near the ground (not shown). Connected.

[Effects] As explained above, in the zero-sequence current measurement method of the present invention, three electro-optic effect elements are used to convert each phase current of a three-phase distribution line into a voltage value and apply it to each element, The zero-sequence current is measured by passing one projected light through each of the above elements in series and electro-optically detecting the balance or unbalance of the current between them. By using the , it is possible to perform measurements while being reliably insulated from the ground potential, and the optical fibers, voltage sensors including electro-optical effect elements, and signal processors used can also be compact, making it possible to It does not spoil the aesthetic appearance like using shape-changing currents.

[Brief explanation of the drawing]

FIG. 1 shows an example of an apparatus used to carry out the present invention. FIG. 2 is an explanatory diagram of the implementation of the present invention. FIG. 3 shows a conventionally used zero-phase current transformer. FIG. 4 is an explanatory diagram of the installation of a zero-phase current transformer in a three-phase overhead distribution line. 1.2.3... Search coil, 4... Housing, 5...
・Voltage sensor, 6... Polarizer, 7... Electro-optic effect element, 8...! /4 wavelength plate, 9... analyzer, 10.
I+...optical fiber! 2...Signal processor. 0・O

Claims (1)

[Claims] (i) A search coil is placed on the side of each of the three-phase overhead insulated wires forming the three-phase overhead distribution line to convert the current of each overhead insulated wire into a voltage signal, and a polarizer and corresponding analyzer are installed. 3 electro-optic effect elements and 1/4 between
A voltage signal from the search coil is applied to the electro-optic effect element of the optical voltage sensor including a wavelength plate, and the projected light from the polarizer is passed through the three electro-optic effect elements and the quarter-wave plate, and the 1. A zero-sequence current measuring method using an electro-optic effect element, which comprises receiving light through an analyzer and converting the received light into electricity through an optical fiber.